This invention relates to articulations of an industrial robot, and more particularly to a device for supporting the driving shafts of parallel linked first and second arms into axial alignment, and applying a pressure prior to the operation of the robot.
In a case where the driving shafts of a first arm and a second arm of a parallel-linked construction are arranged in axial alignment, and operated in high precision, a prepressurizing control is required for eliminating play of the bearings which support the driving shafts of arms from the base structure of the robot.
For instance, in a conventional robot shown in FIG. 5, a parallel link construction is formed by a first arm A, second arm B, third arm C and a fourth arm D, and the driving shafts of the first arm A and the second arm B are rotatably supported by a pair of supporting posts F projecting from the base structure of the robot. FIG. 6 is a cross-sectional view taken along the line X--X in FIG. 5. In this drawing, numerals 1 and 2 designate the supporting posts, numeral 3 designates the first arm, one end of which is secured to .or formed into a frame structure 4 extended between the supporting posts. Numeral 5 designates a driving motor for driving the first arm 3. The driving motor 5 rotates a driving shaft 7 of the first arm 3 through a speed-reduction mechanism 6. The driving shaft 7 is coupled to the supporting frame 4 of the first arm 3. Numeral 8 designates a bearing through which the supporting frame 4 is supported from the supporting post 1. The bearing 8 is preferably made of a cross-roller bearing which is described hereinafter in more detail with reference to FIG. 6(a). The bearing 8 has an inner race fixed to the supporting frame 4, while the outer race thereof is divided into two pieces for applying a pressure to a rolling member of a cross-roller shape. Numeral 9 designates a pressing plate adjustably secured to an appropriate position of the supporting post 1 by means of adjusting screws 10. The plate 9 presses one of two pieces of the outer race to the other. Numeral 10a designates a securing ring which secures the inner race of the bearing 8 onto the supporting frame 4. In the conventional construction shown in FIG. 6, another driving motor 12 is mounted on the supporting post 2 for driving a driving shaft 14 of the second are 11 through another speed-reduction mechanism 13. The driving shaft 14 is rotatably supported by the supporting post 2 through another bearing 15 similar to the bearing 8. The inner race of the bearing 15 is fixed to the driving shaft 14, while the outer race divided into two pieces is secured to the supporting post 2. Another pressuring plate 16 is adjustably secured to the supporting post 2 by means of adjusting screws 17 so that one of the two pieces of the outer race is pressed toward the other. Still another bearing 18 of an ordinary construction is provided for supporting one end of the supporting frame 4 on the circumferential surface of the driving shaft 14.
The supporting frame 4 of the first arm 3 provided between the supporting posts 1 and 2 has one end coupled to the driving shaft 7 and supported through the bearing 8 by the supporting post 1, and the other end supported through the bearing 18 by the driving shaft 14 of the second arm 11. The driving shaft 14 of the second arm 11 is in turn supported through the bearing 15 by the supporting post 2. In order to impart rigidity to the supporting mechanism of the first arm 3 and the second arm 11 and to assure a precision operation of the mechanism, it is required to remove excessive play of the bearings 8 and 15. However, the inner races of the bearings 8 and 15 are fixed to supporting frame 4 and the driving shaft 14, respectively, and therefore one of the two pieces of the divided outer races of the bearings 8 and 15 must be pressed toward the other by the pressurizing plates 9 and 16 which are adjustably secured to the supporting posts 1 and 2 by means of machine screws 10 and 17.
One example of the cross roller bearing used for such purpose is illustrated in FIG. 6a. In the drawing, numeral 81 designates an inner race, 82a and 82b designate an outer race divided into two pieces, and numeral 83 designates a cross roller of a ring-shape. The surfaces 86a and 86b of the cross-roller 83 are held in line contact with the inner and outer races, for rotatably supporting the supported member relative to the supporting post and the like. Numerals 84a, 84b designate dust preventing seals, while numerals 85a and 85b designate bolt-nut combinations which combine the two pieces of the outer race with each other.
On the other hand, the pressing plates are provided for the above described bearings supporting the driving shafts of the first and second arms, respectively, for adjusting the pressures applied to the bearings.
The above described conventional construction requires the bearings of an expensive type such as the cross-roller bearings, and furthermore a pressing plate must be provided for each of the bearings. As a consequence, not only the construction of the device is complicated and the production cost thereof is increased, but also the adjustment of the pressing plate has been troublesome and required much labor.